1. Field of the Invention
The present invention relates to the technical field of image processing and, more particularly, to a video decoding and transcoding method and system.
2. Description of Related Art
Typically, when transmitting an audio-video stream, it requires performing a video transcoding on the audio-video stream in order to convert and reduce the frame rate or resolution of the audio-video stream for transmitting in a congested network. The video transcoding typically reduces the frame rate of a compressed motion image data to become another compressed motion image data. Accordingly, the alternate rate of frames is reduced to further reduce the bit rate of the compressed motion image data for overcoming the insufficient bandwidth in video transmission.
FIG. 1 is a block diagram of a conventional video decoding and transcoding system. As shown in FIG. 1, for eliminating a complex control circuit, a video stream decoded by a decoding unit 110 is stored in a first memory 120 and a second memory 130 respectively. A displaying unit 140 reads the decoded frames of the video stream stored in the first memory 120 for display. A transcoding unit 150 reads the decoded frames of the video stream stored in the second memory 130 for transcode. Accordingly, three frame buffers are required respectively by the first memory 120 and the second memory 130 for display and transcode. Such an implementation can eliminate the complex control circuit. However, it requires a great of memory bandwidth and space.
FIG. 2 is a block diagram of another conventional video decoding and transcoding system. As shown in FIG. 2, for saving the required memory, the system uses a memory 220 with three frame buffers. A displaying unit 230 also sends the displayed frames to a transcoding unit 240. Accordingly, using the memory 220 with three frame buffers and a bandwidth with one memory access capability is enough for the operations.
However, such a system is limited in use due to the requirement of same display and transcode specifications. When the display and the transcode specifications are different, the transcoding operations present certain problems. For example, if a displaying speed of 25 frames/sec and a transcoding speed of 30 frames/sec are used, the collision is presented in memory use since the memory 220 contains three frame buffers only. In addition, if the brightness of a displaying frame is increased on displaying, the brightness of a corresponding transcoding frame is different from that of the displaying frame.
Therefore, it is desirable to provide an improved method to mitigate and/or obviate the aforementioned problems.